1. Field of the Invention
The present invention relates to a radiation measuring apparatus used in atomic energy facilities or the like, and capable of measuring radiation by means of few measuring devices without requiring use of power sources, electronic circuits, etc. in places of measurement, and of carrying out high-efficiency multipoint measurement at low cost.
2. Description of the Related Art
In atomic energy facilities including atomic power stations, stationary radiation detectors are installed in a minimum number of places where radiation measurement is required, and portable radiation detectors, survey meters, etc. are used as required in other places.
A stationary or portable radiation detector requires power a supply for detector biasing, preamplifier biasing, a signal transmitter circuit, etc., and besides, signal transmission cables, power cables, etc.
A portable survey meter, which may be of a chargeable type, must be carried by an operator in charge of radiation control or the like, thus requiring operations for reading and recording measured values during measurement. In a high-radiation atmosphere, moreover, the operator is in danger of nonnegligible exposure to radiation. This portable meter cannot enjoy a high operating efficiency on account of its itinerant service. Moreover, it is almost impossible to measure beforehand the level of radiation dose in a very-high-radiation area or restricted area.
Possibly, this problem may be solved by locating radiation measuring apparatuses in all necessary points of radiation measurement. If the points of measurement are increased, however, the measuring apparatuses, power units, signal transmission cables, power cables, etc. must be increased in proportion in number. Thus, incidental devices are increased, entailing increases in cost of construction and installation, as well as of operation and maintenance. In consequence, this method is hardly practicable.
In long-distance data transmission, electrical signals must be temporarily digitized or converted into light energy. Thus, electronic circuits are needed in various positions, so that there may be aroused problems of magnetic induction noises and ground loops which are attributable to ground potential differences, in some cases.
Since the electronic circuits are arranged in the vicinity of detectors, moreover, the reliability of the apparatuses is lowered by the irradiation effect of semiconductor devices in a very-high-radiation area. In many cases, therefore, the apparatuses cannot be used appropriately.
Accordingly, a method has been tried in which lights generated by the incidence of radiation are transmitted directly or indirectly to optical fibers by means of scintillators as detectors, without requiring use of power sources and electronic circuits in places of measurement. FIG. 39 shows a conventional scintillation detector 23 of a light transmission type used for detection. A scintillator 10 is covered by a reflector 9 and sealed in a housing 8. A fluorescent fiber 24 is embedded in the scintillator 10, and is fixed to an optical connector 13 which is mounted on one end of the scintillator 10. The optical connector 13 is fitted with an optical fiber (or a bundle of optical fibers) 2 which has a rod lens (collimator lens) 12 on its distal end. Fluorescences generated by the absorption of scintillation lights are transmitted through the optical fiber 2 to a photoelectric transfer element 5. In this stage, the fluorescences are converted into electrical signals and processed by means of a signal processing element 6.
The scintillation detector 23 of the light transmission type shown in FIG. 39 constitutes a measuring system which does not require use of electronic circuits and power sources in places of measurement, and will not be affected by magnetic induction noises. If the measuring system of FIG. 39 is used for measurement in a plurality of spots, however, it requires use of a plurality of photoelectric transfer elements 5 and signal processing elements 6. In this case, as shown in FIG. 40, a plurality of scintillation detectors 23 of the light transmission type are located in the individual places of measurement, and lights are transmitted from these places to the locations of measuring devices by means of the optical fibers 2 for transmission. The photoelectric transfer elements 5 and the signal processing elements 6 must be provided corresponding in number to necessary systems in these locations, and a large number of measuring devices are required in the places of measurement.
In the scintillation detector 23 shown in FIG. 39, moreover, the reflector 9 is located on one side of the fluorescent fiber 24. Since perfect specular reflection is difficult in practice, however, some of the generated fluorescences may be wasted- As a result, the signal-to-noise ratio of the system is lowered, so that the lower limit of energy of objects of measurement may be heightened in some cases.
FIG. 41 shows a radiation distribution measuring method using a scintillating fiber, developed as another measuring system of the light transmission type. The scintillating fiber 25 is laid out in a section for an object of measurement, and a photoelectric transfer element 5 is provided at each end of the fiber 25. Some modifications of this measuring method are proposed such that quartz fibers, which entail low optical attenuation, are joined together in use.
In the case where the object of measurement is the gamma-radiation distribution in atomic energy facilities or the like, for example, however, this measuring method involves various problems, such as low detecting efficiency, and cannot be easily put to practical use.